I checked English to English answers of 'seamless' and like Mr Saleh I found Jccantrell's answer relevant and correct. In sum, according to Jccantrell's, "What I understand is that this school runs K-12 under one administration, in one set of buildings at one location. This is what I understand with seamless." So 'seamless' is a school that teaches up to K- 12, that it is both school and college in Bangladesh system. You see we have in Bangladesh some schools that have college sections like Viqarunnisa Noon School and College or Holy Cross School and College and there is no term like 'seamless' that describes 'both school and college' section and that is why we call simply 'school and college'.

Although, 'akhondo' (অখণ্ড) is a good Bangla but does it necessarily convey the intended meaning to Bengali audience who are not aware of US school system? Therefore, I think it is difficult to have a suitable Bengali term for 'seamless' for one must recognize that all languages and cultures do not have same equivalent terms and concepts. So I suggest an explanatory translation of the term 'seamless'. As I do not know the following words, you can say 'amader protishthanti ekti laboratory school o college....' (আমাদের প্রতিষ্ঠানটি একটি স্কুল ও কলেজ....)


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Note added at 6 days (2006-07-31 06:54:08 GMT)
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To avoid any confusion, I would like to add here that 'স্কুল ও কলেজ' (school o college) should in no way be considered as meaning of 'seamless', rather it is a translation suggestion solely for this particular context.

'obichchinna' or 'okhondo' is good Bangla for 'seamless' when it is put separately or in relevant context as such cloth, as it is suggested in Bangla Academy Dictionary.

'Collegiate school' can be an option.